As demands on a rubber mixture increase in various manufacturing fields such as a tire, impact resistant polystyrene, the sole of a shoe, a golf ball, etc., the value of a butadiene rubber which is an intermediate of petrochemicals increases as an alternative material of a natural rubber of which production is insufficient.
However, as the costs of the main material of the butadiene rubber increases depending on high oil prices, the burden on increasing the prime cost of a synthetic rubber is added.
To decrease the prime cost of the butadiene rubber, development on processing technique of the butadiene rubber is necessary along with the building of additional factories for producing the butadiene rubber.
The butadiene rubber is known to be manufactured by a polymerization system using a catalyst containing a rare earth metal. Particularly, a neodymium compound (Nd(OOCR)3, R=alkyl group) is verified to be particularly effective among the catalysts including the rare earth metal (See Patent Document 1).
However, the catalytic activity of the neodymium compound is at most 7% (See Non-patent Document 1). This result may be obtained due to the following. A common neodymium carboxylate compound is prepared in an aqueous solution and then is extracted using an organic solvent, and neodecanoate is included therein as a ligand. Thus, a large amount of the neodymium carboxylate compound having an oligomer type is present in the product thus obtained. That is, due to the structure of the oligomer type, the production yield of a catalyst active species may be deteriorated, and the catalytic activity may be decreased when used as a catalyst for diene polymerization.